Suicide

Suicide is when a monster attacks another with an equal or more ATK; also called "ramming".

This is often called a KO (knock out) or a Double KO if both monsters get destroyed. This can be used tactically to activate effects that only work when a monster is sent to the Graveyard by battle, such as those of "Mystic Tomato" or "Pyramid Turtle". The loss to your Life Points is often worth the field advantage you gain through those effects.